1. Field of Invention
This invention relates to a method for the treatment of exhaust gas streams, and, in particular, to a treatment of exhaust gas from a chromium plating plant for the removal of liquid droplets containing chromium salts from the exhaust gas.
2. Brief Statement of the Prior Art
Electroplating operations are extensively used in various industrial applications for imparting a polished surface and/or surface hardness to metal objects. One commercial application of this process is the electroplating of chromium on crankshafts such as the large crankshafts used in large diesel engines for locomotives.
Electroplating vessels used in chrome plating of locomotive crankshafts typically have dimensions from about 14 to 18 feet in length and approximately 3 feet in width and, thus provide a relatively large vapor liquid surface for the entrainment of liquid droplets of the electroplating solution. The environmental problems of such operations is heightened by potential toxicity of salts which are carried into the exhaust gas from such operations. In this regard, hexavalent chromium is recognized as having a relatively high toxicity and, accordingly, diligent efforts must be maintained to limit or curtail the discharge of any hexavalent chromium into the atmosphere with the gases discharged from such electroplating operations.
Various techniques have been used for the removal of liquid droplets from gas streams. Equipment which has been used with limited success includes wet cyclone separators, bag houses, filters, etc. One of the challenges to any such operation is the extremely high efficiency which is required of any filtration system when applied to the aforementioned electroplating operations. Regulations applicable to such operations conducted in metropolitan areas require the removal of at least 99.8% of the entrainment carryover from the exhaust gas. In other words, the removal efficiency must be at least 99.8% or greater to permit the application of the gas treatment method and continuation of the electroplating process.